The invention described herein was made in the performance of work under a NASA contract, and is subject to the provisions of Public Law 96-517 (35 U.S.C. 202) in which the Contractor has elected to retain title.
The present invention relates to semiconductor imaging sensors, and more particularly, to semiconductor imaging sensors having on-chip encryption capabilities.
Semiconductor imaging sensors have been used in a wide range of imaging applications. Images captured by a sensor can be converted into digital form for imaging processing or storage. Development in data processing and communication devices and systems allows easy and convenient transmission and exchange of digital images or video through various electromagnetic transmission channels (e.g., telephone lines and coaxial cables) and portable storage media (e.g., optical or magnetic disks).
Privacy or security of digital images is desirable in many applications. In particular, exchange and transfer of digital images over a shared transmission channel present a challenge to the security of sensitive information. Internet and Intranet are two examples of such a shared information transmission channel in which many computers are connected with one another by local or wide area communication networks. It is possible for a third party or an intruder to intercept or tamper with an digital image that is transmitted through such a shared transmission channel.
Data encryption techniques have been developed to increase the security or privacy of digital data or images by encoding the data to limit unauthorized access. An encryption technique uses a xe2x80x9ckeyxe2x80x9d based on a particular algorithm to change the sequence or format of digital data or images (xe2x80x9cplaintextxe2x80x9d) so that the data or image is enciphered or xe2x80x9cscrambledxe2x80x9d into an unintelligible form (xe2x80x9cciphertextxe2x80x9d). An authorized user recovers the scrambled data or image by using a xe2x80x9ckeyxe2x80x9d that is constructed based on the encryption method. However, an unauthorized user, who does not have the knowledge of either the encryption method (e.g., the encryption algorithm) or the key, cannot easily decode the information.
The keys may be a non-rigid type which allows the same encryption and decryption functions to be used with different keys. Rigid type keys are xe2x80x9cfixedxe2x80x9d into hardware and are desirable in certain types of turn-key systems where data transfer is mostly in one direction (transmission only).
Cryptosystems may be divided into two main categories, symmetrical systems (i.e., the private key systems) and asymmetrical systems (i.e., the public-private key systems). The former is based on functions which may be easily computed but for which it is computationally infeasible to compute the inverse functions. The latter uses a secret key which is shared by the communicants and an eavesdropper has to decipher this secret key among extremely large amount of possibilities.
One well-known symmetrical encryption system is the Data Encryption Standard (xe2x80x9cDESxe2x80x9d) which exploits confusion and diffusion techniques. The number of DES keys can be up to or longer than 512 bits with the current computational power and as short as 64 bits with a security level acceptable to many applications. The DES cryptosystem typically encrypts 64-bit blocks of plaintext using a key length of 56 bits. The fundamental building block in DES (referred to as a round) is a combination of a substitution and a subsequent permutation of the text, based on the key. The plaintext is encoded through 16 rounds of a function, which usually implements substitution, permutation, exclusive-OR (xe2x80x9cXORxe2x80x9d), and shift operations on subsets of the text and the key. In each round, a different subset of the elements from the key are used to perform the encryption. Hence, for example, a key K1 may be applied during the first round, and a key Ki is applied during the ith round, etc. An analogous algorithm is used to decrypt the ciphertext, but the keys are now applied in reverse order, and the shift operations are also performed in the opposite direction.
Another cryptosystem is the asymmetric RSA (xe2x80x9cRivest-Shamir-Adlemanxe2x80x9d) Public Key Cryptosystem. See, Rivest et al., xe2x80x9cOn digital signatures and public-key cryptosystems,xe2x80x9d Comm. Of the ACM, Vol. 21, pp. 120-126, February, 1978. Two different keys are used: a public key to encrypt the plaintext and a private key to decrypt the ciphertext. Hardware implementations of RSA are usually many orders (e.g., about 1000 to 10,000 times) slower than a respective DES implementation. In software implementations, RSA is generally about 100 times slower than DES. As a result, RSA is often used for secure key exchange without prior exchange of secrets. Digital data or images are encrypted with DES. The encrypted data or images are sent out with the DES key encrypted by using RSA public key encryption.
In addition to encryption, it also desirable in certain applications to ensure the validity of a digital image. Validity of images has been traditionally checked by visual inspection for clues such as internal consistency, documentable provenance, and consistency with existing beliefs. Certain digital manipulation and synthesis of images may be free of observable defects. One way to indicate the originality and validity is to superimpose a digital signature on a digital image prior to transmission or transfer.
Conventional implementations of the above image encryption techniques usually use encryption circuitry separate from the imaging sensor chip. This may compromise the security of the image data since the image data can be intercepted or tampered during transmission from the imaging sensor chip to the off-chip encryption circuitry.
The present invention integrates one or more analog-to-digital converters and encryption circuity on a focal plane of a semiconductor imaging chip to achieve on-chip encryption and/or superimposition of a digital signature.
A semiconductor imaging device according to one embodiment of the invention includes an imaging array with a plurality of sensing elements formed on a semiconductor substrate, at least one analog-to-digital converter formed on the substrate and electrically connected to the imaging array, and an encryption circuit formed on the substrate. An optical image received by the imaging array is converted to a digital image by the analog-to-digital converter. The encryption circuit encrypts the digital image according to an encryption key to produce an encrypted digital output.
An electronic circuit may also be formed on the substrate to produce a distinct digital number associated with the imaging device. The digital number can be superimposed on the digital image as a digital signature of the device.
These and other aspects and advantages of the present invention will become more apparent in light of the following detailed description, the accompanying drawings, and the claims.